Expand the configuration API to allow dynamic runtime load and unload of
configurations and features.

On load, configurations and features are tagged with a "load owner" that
is used to determine sets that were loaded together in a given API call.

To unload the API uses the load owner to unload all elements previously
loaded by that owner.

The API also records the order in which different owners loaded
their elements into the system. Later loading configurations can use
previously loaded features, creating load dependencies. Therefore unload
is enforced strictly in the reverse order to load.

A load owner will be an additional loadable module, or a configuration
loaded via configfs.
Signed-off-by: Mike Leach <mike.leach@linaro.org>
Link: https://lore.kernel.org/r/20211124200038.28662-3-mike.leach@linaro.orgSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>